This article is about the neuropsychiatric disorder. For the physical malady, paralysis, see paresis.

General paresis, also known as general paralysis of the insane or paralytic dementia, is a now-rare neuropsychiatric disorder affecting the brain and central nervous system, caused by syphilis infection. It had been considered a psychiatric disorder before and during the nineteenth century, when it was first scientifically identified and discovered to be extremely common, because the patient usually first sought—or was brought for—treatment because of psychotic symptoms of sudden and often dramatic onset.

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The diagnosis could be differentiated from other known psychoses by a characteristic abnormality in eye pupil reflexes (Argyll Robertson pupil), and, eventually, the development of muscular reflex abnormalities, seizures, memory impairment (dementia) and other signs of relatively pervasive neurocerebral deterioration.

Although there were recorded cases of remission of the symptoms, especially if they had not passed beyond the stage of psychosis, these individuals almost invariably suffered relapse within a few months to a few years. Otherwise, the patient was seldom able to return home because of the complexity, severity and unmanageability of the evolving symptom picture. Eventually, the patient would become completely incapacitated, bedfast, and die, the process taking about three to five years on average.

While retrospective studies have found earlier instances of what may have been the same disorder, the first clearly identified examples of paresis among the insane were described in Paris after the Napoleonic Wars. General paresis of the insane was first described as a distinct disease in 1822 by Antoine Laurent Jesse Bayle. General paresis most often struck people (men far more frequently than women) between twenty and forty years of age. By 1877, for example, the superintendent of an asylum for men in New York reported that in his institution this disorder accounted for more than twelve percent of the admissions and more than two percent of the deaths.

Originally, the cause was believed to be an inherent weakness of character or constitution. While Esmarch and Jessen had asserted as early as 1857 that syphilis caused general paresis, progress toward the general acceptance by the medical community of this idea was only accomplished later by the eminent nineteenth-century syphilographer Alfred Fournier (1832–1914). In 1913 all doubt about the syphilitic nature of paresis was finally eliminated when Noguchi and Moore demonstrated the syphillitic spirochaetes in the brains of paretics.

In 1917 Julius Wagner-Jauregg discovered that infecting paretic patients with malaria could halt the progression of general paresis. He won a Nobel Prize for this discovery in 1927. After World War II the use of penicillin to treat syphilis made general paresis a rarity: even patients manifesting early symptoms of actual general paresis were capable of full recovery with a course of penicillin. The disorder is now virtually unknown outside Third World countries, and even there the epidemiology is substantially reduced.